why different routes on 2 Oregon 700?? never the same ..

We have 2 origon 700 complete the same, cards, software e.g. But when i  make a trip from a to b they are always different. Also for 3-4 km???

What can i do that they have the same route by a trip??

When I make a route and sand it from one to another also different !!

Thank

Henk